This invention relates to a field of temperature indicating devices, more particularly as applied to the monitoring of room or ambient temperatures by the use of liquid crystals.
Known temperature sensors or thermometers generally consist of colored or opaque liquids such as mercury, enclosed in carefully calibrated glass containers in which the liquids expand and thereby creep up as a thin column along a calibrated transparent tube as they are heated. Some others consist of metal coils to which are attached pointers which are designed to point to calibrations around the coils in the form of dials, advancing around the face of the dials in a circular manner as the metal coil expands and lengthens with increasing heat. These are delicately calibrated and relatively expensive to manufacture. More accurate but more expensive are electonic probes or thermistors.
Liquid crystals have been described and have been used for making room thermometers recently. These crystals are painted or printed on plastic substrates in the form of digital displays. Since they have the property of changing colors at very precise and predetermined temperatures reversibly without appreciable deterioration, they lend themselves for this purpose very advantageously.
All these thermometers indicate and convey the sensed temperature in the form of numeric or digital displays. Readability is limited by the size of the printed numbers. Electronic activation of electric lights for the purpose of displaying the numbers is complicated and expensive. The digital liquid crystals are not printed in great big sizes for they become unattractive eyesores in a room. They add little to enhance the beauty of rooms. References maybe made to U.S. Pat. Nos. 3,533,399; 3,712,141; 3,661,142; British Pat. Nos. 1,161,039 and 1,138,590.